Circuit for recognizing the response of a subscriber in telephone exchanges

Read the whole patent

Listed from its EPO record in Patent Yard's archive of European patents past their term. Its claims, description and drawings are in the EPO PDF and on Google Patents, and the Claude kit works from them.

Why it's free to use

• Filed December 24, 1980 and granted March 14, 1984. A European patent lasts at most 20 years from filing, so its term ended December 24, 2000.
• A supplementary protection certificate, which can extend a medicine or crop-protection patent, adds at most five and a half years, so even that would have ended by June 24, 2006.
• We check European rights only. A US or other national patent in its family could still be in force: check its family on Espacenet or Google Patents.